Packing gland for TiCl4 inlet to oxidizer reactor

ABSTRACT

A fabricated packed pipe coupling gland suitable for a connection where there is at least one brittle pipe, the coupling forming a pressure tight, leak proof coupling which is semi-rigid. The coupling is particularly useful for coupling glass pipe to metal pipe for conveying highly corrosive vapors at high temperature, for example heated titanium tetrachloride vapors to a reactor for forming titanium dioxide.

The present invention relates to a fabricated pipe coupling forconnecting a plain end brittle pipe to a metal pipe or reactor, or toanother similar brittle pipe, where the pipes may be subjected tomechanical and high thermal stresses. The invention more particularlyrelates to such a connection for handling highly corrosive vapors, andmore particularly to a coupling between brittle pipes in process linesfor forming titanium dioxide by the oxidation of titanium tetrachloride.

For sake of illustration, the present inventive pipe coupling will bedescribed in conjunction with the production of titanium dioxide by thevapor phase oxidation of titanium tetrachloride, although it will beunderstood that it is not solely confined to this use.

The vapor phase oxidation of titanium tetrachloride to form titaniumdioxide is described in U.S. Pat. No. 3,512,219. In that process,titanium tetrachloride vapors are heated to a temperature of about800°to 1100°C. before reaction with oxygen in a reactor. The titaniumtetrachloride vapors are highly corrosive at such elevated temperatures.Thus all surfaces which are contacted by titanium tetrachloride vaporsshould be sufficiently inert to reaction with the vapors.

Because of the temperature and corrosion factors, heating of thetitanium tetrachloride vapors has been done in a furnace having glass(fused silica) pipes. The heated titanium tetrachloride vapors arepassed from the glass pipe furnace to a platinum lined metal reactor.Thus the glass pipe must be connected to the inlet of the metallicreactor by a coupling. Previously the connection has been made by usinga short section of glass pipe which has a slightly belled end and hasbeen carefully machined on its connecting end to fit against the metalflange of the reactor, and clamped, with sealing gaskets, by means of aflanged collar. This is called a buttress connection. The short pipe waswelded to the end of the furnace pipe. In order to form a leakproofseal, the clamping pressure is such that it frequently put such stresson the glass pipe so that it broke. Moreover, it has been difficult toform a good leakproof seal by a gasket in the buttress connection, sinceany imperfection in the machined end of the glass pipe will not allowthe gasket to seal perfectly. Another problem is that the coupling mustbe replaced fairly often, and the atmosphere in the vicinity of thefurnace is so heated as to be relatively exhausting to workmen. Thusthere were considerable problems with the buttress connection, sinceoften the connection, once made, would leak and had to be replacedimmediately, with great inconvenience and expense due to the processdown time.

It is therefore an object of this invention to provide a semi-rigid,leak-proof pipe coupling.

A further object is to provide such a coupling which may beprefabricated and more easily installed.

Another object is to provide a pipe coupling that does not have to bemanufactured to close machining tolerances.

A further object is to provide a pipe coupling which will withstand hightemperature and highly corrosive vapors.

These and other objects of the invention will become apparent as thedescription thereof proceeds.

The invention may be more readily understood by reference to thedrawings in which

FIG. 1 shows a cross-sectional view of the inventive pipe coupling,

FIG. 2 shows a cross-sectional view of a pipe coupling according to theprior art,

FIG. 3 shows a cross-sectional side view taken along the lines 3--3 ofFIG. 4 of a variation of the inventive coupling to connect two brittlepipes in a U-bend,

FIG. 4 shows an end view taken along the lines 4--4 of FIG. 3 with partsbroken away of the pipe coupling in FIG. 3,

FIGS. 5 and 6 are plan views of parts of the pipe coupling of FIG. 3,and

FIG. 7 is a schematic view in elevation of the furnace and reactor zonesfor a vapor phase titanium dioxide process.

Referring to FIG. 7, in the production of titanium dioxide by the vaporphase oxidation of titanium tetrachloride, the titanium tetrachloridevapors are fed into the inlet 1 of glass pipes 2 in furnace 3. Pipes 2are composed of a series of U-bends of fused silica pipe. The titaniumtetrachloride vapors are heated to about 1000°C. and leave the furnaceat 4 which is the point where a coupling 5 is made between furnace 3 andreactor zone 6. A section of glass pipe 21 is fusion welded to thefurnace pipes 2 at point 4 and is inserted into a metallic coupling 5.Coupling 5 is connected to metallic reactor 7 by means of a water cooledflanged metallic pipe section 8. It will be clear, however, thatcoupling 5 could be fastened directly to reactor 7. In the process asshown, oxygen is fed to reactor 7, together with the heated titaniumtetrachloride vapors, to produce titanium dioxide. A nitrogen purge gasis passed into the coupling 5 at 31 to prevent vapor leakage from thecoupling, as will be described in greater detail subsequently. In thearrangement described in FIG. 7, it is possible to prefabricate coupling5 including the pipe joing 21, and install it by bolting to reactor 7 atthe flanged end, and welding pipe 21 at point 4. The coupling isremovable by fusion cutting at point 4 and unbolting the flanges.

In FIG. 2, a coupling used by the prior art is shown. A section ofsilica pipe 10 having a machined buttress 11 was bolted to a watercooled flange 12 by a water cooled backing flange 13 buttress insertring 14 and bolts 15 with spring washers 16. The coupling includedgaskets 17 and 18. This gave rigid connection requiring preciseinstallation procedures and preparation of component parts. Face 19 ofbuttress 11 and 20 of flange 12 had to be precisely machined. Itresulted in a fragile connection subject to frequent breaks due tostresses occurring under various operating conditions and to boltingpressure at the buttress 11. Leaks at the flange face 20 were alsocommon since it was not possible to compress gasket 18 sufficientlytight because the necessary pressure might break buttress 11. Inaddition, if faces 19 and 20 were not perfectly machined, the gasket 18would not form a good seal between the faces and leaks occurred.

The problems of the prior art were solved by the use of a packedcoupling as shown in FIG. 1.

Briefly, FIG. 1 is a horizontal cross-section of the packed coupling 5.A length of plain end machined silica pipe 21 is inserted into flangedpacking gland 22 which consists of high temperature packing 23 and oneor more lantern rings 24. An inert gas purge (nitrogen) is used on thelantern rings to prevent hot titanium tetrachloride vapor from leakingbackwards through the packing to the atmosphere. The follower 25 hasspring loading 26 to apply continuous pressure and compensate forexpansion of metal and compression of packing at high temperatures. Theunit is bolted to a water cooled flange 27 at the inlet of a watercooled metal reactor 7. (See FIG. 7) Then the machined pipe 21 is fusionwelded to a length of unmachined glass pipe 2 at the outlet 4 of a firedheater 3. Flange 27 may be part of a water cooled extension 8 (as shownin FIG. 7) to enable installation in an unheated area adjacent to a firebox 6 in which the reactor is located.

Considering the coupling in greater detail, packing gland 22 consists ofa sleeve 28 having a flange 29 at one end and a flange 30 at the otherend. In FIG. 1, gland 22 also has two fluid inlet lines 31 for a purgegas. Flange 29 forms an annular abutment 32 for holding compressiblepacking rings 23. In addition, the internal diameter of flange 29 isslightly larger than the outside diameter of pipe 21, so that there isno contact between them. In assembling the coupling, the section offused silica pipe 21 is inserted into gland 22 leaving a space 33 at theface of flange 29. Packing rings 23 and metallic lantern rings 24 arethen inserted into the annular space between the outside of pipe 21 andthe inside of gland 22. The number of packing rings will be such thatthe lantern rings are spaced opposite the openings of inlet lines 31.The metallic lantern rings 24 have an inside diameter slightly largerthan pipe 21, and are annular perforated rings which admit purge gas tothe packed annular space between gland 22 and pipe 21. Follower 25 isthen placed over pipe 21 and inserted into gland 22 until it contactspacking 23. Follower 25 consists of a sleeve 34 and flange 35, sleeve 34having an inside diameter slightly larger than the outside diameter ofpipe 21. Bolts 36 are inserted into springs 26 and through flange 35 offollower 25 and flange 30 of gland 22. The bolts are then tightenedsufficiently to compress packing rings 23 so that pipe 21 is held solelyby the pressure of the packing rings and is not in contact with anymetal parts of the coupling. It has been found that this may be donewith a torque of 120 pounds on the tightened bolts. The packed couplingis less rigid, is more easily installed and can absorb shocks withoutfrequent breaks. The spring loading and nitrogen purge prevent leakswhich could cause air pollution and corrosion damage problems. Theprefabricated packed coupling can be installed by bolting flange 29 toflange 27 with a gasket 37 between the flange faces by means of bolts38. Since there is no fragility at this point, bolts 38 may be tightenedas much as possible to form a gas tight seal at gasket 37. Theinstallation of the coupling is completed by fusion weld pipe 21 to pipe2, by known methods. The titanium tetrachloride vapors, which arenormally under a pressure of about 5 p.s.i.g., are prevented fromescaping through the coupling by the combination of packing rings 24,and the purge gas which is fed into lantern rings 24 at a pressure ofabout 10 p.s.i.g.

In the titanium dioxide process the metallic follower 25, gland 26 andlantern rings 24 are of high heat and corrosion resistent metal such asa high nickel alloy, having at least 60% nickel, e.g. Nickel 200, Nickel201, Inconel 600, Inconel 625, and the like, (as made be InternationalNickel Co.). Lines 31 and bolts 36 and 38 and springs 26 may bestainless steel. The bolts and springs may be ordinary carbon steel,except that they may not be reusable then. Gasket rings 23 are of a heatand corrosion resistent material such as graphite or fiberglass, e.g.Refrasil fiberglass packing (as manufactured by H. I. ThompsonFiberglass Co.). Gasket 37 between flanges 27 and 29 may be of asuitable heat and corrosion resistent material, e.g. asbestos.Modifications designed to provide additional protection of metal againstmore corrosive substances and/or higher temperature by using coolingjackets or protective linings do not change the basic design of theapparatus. Likewise, the number or type of lantern rings or packingrings as well as the type of purge gas can be varied to provideadditional protection of packing and construction material or to meetsealing requirements. For instance, there are some applications in whichpurge gases other than nitrogen would be more readily available or morecompatible with the system. There are some applications at lowertemperatures in which the metallic parts and packing could be varied.The unit can be easily modified to couple two sections of brittle pipetogether by having a packing gland at both ends of the unit (as when twounits are bolted together back to back).

One embodiment of the invention used to connect two brittle pipestogether is shown in FIGS. 3 to 6. The coupling is for a U-bend such asthose in the silica pipe 2 in furnace 3. Because of the hightemperature, the pipe bends are subject to movement resulting inbreakage, particularly in the sections of pipe closest to the outlet offurnace 3. By use of a U-bend coupling as shown in FIGS. 3 to 6, pipe 2is given some flexibility so that breakage is not as likely to occur.The basic principal of the U-bend coupling is essentially similar tothat illustrated in FIG. 1. A silica pipe 121 is inserted into a packinggland 122 with packing rings 123. A follower 125 fits into gland 122against packing 123 and is bolted at flanges 130 and 135. In thisembodiment, flange 130 is an elongated plate 140 haaving two packingglands welded thereto. Flange 135 is an elongated plate 141 having twofollower sleeves 125 which fit into the two packing glands 125. Flanges130 and 135 are bolted together at 142. The U-bend silica pipe section143 is contained in a metallic housing 144 having a flange 145 withelongated opening 146 which is securely bolted to follower flange 135,with a gasket 137 between the flange faces. Pipes 121 are inserted sothat they do not make contact with U-bend pipe 143. No purge gas meansis shown since it is not necessary at this point. The U-bend couplingallows flexing and temperature compensation in the furnace pipespreventing breaking of the pipes.

While the coupling has been described as useful in the vapor phaseoxidation of titanium tetrachloride to produce titanium dioxode, thissame basic design is suitable for use with a wide range of materialsother than the titanium tetrachloride used here. It can also be adaptedfor much higher temperature operation by simply fabricating a coolingjacket for gland body and/or follower. This type modification would,also, enable installation in a heated firebox. Protective coatings canbe used to handle more corrosive materials. The unit can easily be foruse in coupling two sections of brittle pipe. A wide variation ofpacking materials or alloys is available depending on the specificapplication. The packing inventive gland coupling provides a superiorseal, is much less rigid and is more easily installed than the standardbuttress type of connection. Therefore, it is less subject to leaks andbreaks due to stresses which occur during startups, shutdowns and systemupsets as well as normal operations.

We claim:
 1. Pipe coupling means for coupling brittle pipe comprising aouter metallic sleeve means having a flange at each end, means on one ofsaid flanges to form an immovable connection to other conduit means, aplurality of packing rings within said sleeve, at least one metalliclantern ring means interspersed in said packing rings, means tocontinuously admit a purge gas to said lantern ring under pressuregreater than that within said brittle pipe, packing retaining meanswithin said sleeve adjacent one of said flanges, a flanged metallicfollower sleeve means fitting within said outer sleeve, said couplingmeans receiving a brittle pipe of less outer diameter than the insidediameter of any metallic means, means connecting said follower flange tosaid other sleeve flange means to urge said follower against saidpacking and said packing against said packing retaining means, saidmeans providing sufficient force to expand said packing thereby holdingsaid brittle pipe in spaced relation from said metallic means.
 2. Thecoupling of claim 1 including at least two lantern rings.
 3. Thecoupling of claim 1 wherein said brittle pipe is a short section and isa part of said coupling. k
 4. The coupling of claim 1 wherein saidurging means is a plurality of spring loaded bolts through said followerflange and the adjacent sleeve flange.
 5. The coupling of claim 1including a section of flanged, jacketed fluid cooled metallic conduitattached at the sleeve flange of said coupling away from said brittlepipe, a gasket being between said flange faces.
 6. The coupling of claim1 wherein said brittle pipe is a silica pipe.
 7. The coupling of claim 1wherein said packing is thermally and chemically resistent.
 8. Thecoupling of claim 7 wherein said packing is fiberglass.
 9. The couplingof claim 1 wherein said sleeve, follower and lantern rings are of athermally and chemically resistent metal alloy.
 10. The coupling ofclaim 1 wherein said alloy is a high nickel alloy.